This invention relates to a microporous particulate filter capable of removing micron, sub-micron and molecular particulate from a pressurized continuous gas stream. The filter has a wide range of application in the medical and dental fields, food industry and in the manufacture of electronics.
The importance of air and medical and dental gas has become a much more critical consideration in the recent past as a result of the development of Acquired Immunodeficiency Syndrome (AIDS) as a serious public health concern. Since the method of transmission is still incompletely understood, any means by which air or any other gas contaminated with AIDS or another infectious disease comes into contact with the bloodstream of a patient must be carefully scrutinized to reduce the possibility that the infection is being inadvertently transmitted.
The invention has a particular application to the filtration of bacteria and viruses from gases. For example, in medical and dental fields the filter has application in the centralized and point of use filtration of medical air and gas streams used in respiration therapy, in the filtration and collection of potentially harmful infectious particulate from vacuum system effluent discharge, and in centralized and point of use filtration of anesthesia gas streams.
Filtration removes potentially harmful particulate which if left unfiltered could increase risk of patient infection. The integral nature of the filter disclosed in this application reduces the possibility that improper handling and disposal of the effluent discharge can cause disease transmission.
In dental applications, there is a perceived danger from circulation, compression and reuse of air directed into the mouth of a patient, where contaminants may enter the bloodstream. The problem is aggravated because compression of unfiltered atmospheric air from within the dental environment has the effect of concentrating any contaminants present. Filtration of the air within a medical or dental environment also removes potentially abrasive particulate matter which could damage internal working parts of instruments, thereby shortening their working life.
In the food industry, filtration of solids and potentially infectious particulate from compressed air used in processing and dispensing food and beverages reduces the possibility of contamination by contact between the food and the air.
In the electronics industry, removal of micron and sub-micron particles from atmospheric air reduces possibility of these particles contaminating semiconductor and similar components.
The preferred filter medium used in the filter disclosed in this application is a microporous hollow fiber such as Celgard (.TM.) microporous hollow fiber manufactured by Questar division of Celanese Corporation. Technical information, fabrication and handling information concerning this fiber can be found in a Celanese bulletin entitled Technical Information, Fabrication & Handling--Hollow Fiber, March, 1985. This fiber is formed of polypropylene polyolefin resins. This product has heretofore been used in electrochemical systems, batteries, electronic devices, sterile packaging, medical devices and a variety of industrial and biotechnical applications, as well as supports in immobilized liquid and thin film membranes. The hollow fiber offers controlled and relatively uniform porosity as compared with asymmetric ultrafiltration/microfiltration membranes. The fiber is resistant to acids and bases and is permeable to gases and vapors. The geometry of the hollow fiber offers a compact size because of the high membrane surface area-to-volume ratio. The fiber resists fouling due to shear forces generated during flow through the fiber lumen and is self-supporting.
The fiber surface is comprised of a series of parallel slot-like pores. These pores form tortuous, interconnected channels leading from one surface of the fiber to the other. The pores allow the flow of gases and vapors but block passage of many bacteria, colloids and other sub-micron particles and solutes. The pore structure of the fiber is relatively uniform and homogeneous from one side of the fiber wall to the other. This is in contrast to asymmetric membranes wherein the pore width increases by orders of magnitude as it progresses from side of the membrane to the other.
Because this fiber is known to pass vapors while blocking passages of liquids, it has heretofore been used to separate blood proteins, macromolecules and cellular material from blood, and to infiltrate oxygen into blood in blood oxygenators. It has also been applied to pollution control problems and recovery of byproducts. Insofar as is known, the fiber has not been heretofore used to filter sub-micron and molecular matter from gases, such as air and medical/dental gases.
Many viruses have a size much smaller than the average pore width of the hollow fiber--0.04-0.05 microns. Polio virus, because of its extremely small size is considered a good test of the ability of a filter material to filter viruses. Surprisingly, it has been determined by laboratory analysis that polio virus is filtered to an extremely high degree of efficiency by the hollow fiber used in the present invention. This is believed to be caused not only by the tortuous, three-dimensional path through the fiber wall but by an affinity of the fiber for the matter which impacts the side walls of the pores as it transits the pores from one side of the fiber wall membrane to the other.
This invention makes effective use of the characteristics of the hollow fiber in combination with a mechanical system which permits safe operation and disposal of the filter.